The need for measuring and recording physiological pressures, for example, in the coronary vessels, has triggered the development of miniaturized devices for enabling the access to the very narrow vessels, such as coronary vessels. Typically a sensor of very small size is mounted on a guide wire, which is inserted in e.g. the femoral artery and guided to the desired point of measurement, e.g. a coronary vessel. There are certain problems associated with the integration of a pressure sensor onto a guide wire suitable for the type of measurements mentioned above. The first and foremost problem is to make the sensor sufficiently small. Also, the number of electrical connections and leads should be minimized, in order to obtain a sufficiently flexible guide wire which can be guided to the desired location through the coronary vessels without too much difficulty. One way of eliminating the electrical leads and connections is to employ a resonance sensor which reacts on external stimuli in the form of e.g. ultrasonic energy by emitting a resonance frequency that can be correlated to pressure prevailing in the environment where the sensor is located. Such a device is disclosed in our co-pending U.S. patent application, Ser. No. 09/219,798, filed Dec. 23, 1998, and whose entire contents are incorporated herein by reference.
Another example is disclosed in U.S. Pat. No. 5,619,997 (Kaplan). It relates to a passive sensor system using ultrasonic energy, and comprises an implantable sensor capable of responding to ultrasound by emitting a resonance that is detectable and which varies in accordance with the variations of a selected physical variable.
A drawback with these systems is that they require an external source of ultrasonic energy, which is located outside the body in the vicinity of the measurement location. It makes the systems bulky and it may be difficult to accurately know the position of the resonance sensor inside the body, and thus the quality of the signal can be less than optimal.
Therefore, the object of the present invention is to provide a system that overcomes the drawbacks indicated above.
This object is achieved with a resonance pressure transducer system as described below. Thereby, a resonance sensor is arranged in close proximity to, preferably mounted on, a source of ultrasonic energy, e.g. a piezo-electric crystal capable of generating oscillations in the frequency range 10 kHz to 100 MHz.
Preferably the system is provided on a wire, e.g. a guide wire, to facilitate insertion into the body of a patient.
In a further aspect of the invention there is provided a pressure measurement system, comprising an AC power supply; a resonance based pressure transducer system; and a control unit for controlling the supply mode of the AC power, and for analyzing a resonance signal emitted from the resonance based pressure transducer system.